Experience from start-up and operation of deammonification MBBR plants, and testing of a new deammonification IFAS configuration

Summary

A single-stage deammonification process utilizing biofilms on moving carriers in a mixed reactor (ANITA™Mox) is studied. Partial
nitritation and autotrophic N-removal occur simultaneously within the biofilm, where aerobic and anoxic zones result from oxygen mass transfer limitation. Ammonium oxidizing bacteria (AOB) oxidize NH₄ to NO₂ in the aerobic zone of the biofilm (i. e. external biofilm) while Anammox bacteria (AnAOB) located in the anoxic zone of the biofilm (i. e. internal biofilm) consume NO₂ produced by AOB together with the excess NH₄. The process has been implemented at full-scale as a Moving Bed Biofilm Reactor (MBBR) to treat reject water from dewatering of digested sludge. Startup of these installations was accelerated using a seeding strategy whereby 3–15% of carriers with established AOB/AnAOB biofilm were mixed with new carriers. N-removal rates up to 1.2 kgN/(m³react·d) have been observed in the full-scale process. The achievable rate is influenced by substrate transport inside the biofilm, which depends on factors such as biofilm density, thickness, temperature, and substrate concentrations. One possible strategy to increase the N-removal is to enhance substrate transport. Using Integrated Fixed-Film Activate Sludge (IFAS) to separate the nitritation and anammox reactions spatially, instead of adjacent in the same biofilm, allows the AOB to grow in suspended phase to better utilize DO, while allowing the biofilm to specialize in AnAOB reaction to achieve higher rates. A lower bulk DO can be used in this mode. Results from full-scale ANITA™Mox MBBR treating sidestream effluent are presented together with preliminary ANITA™Mox IFAS results from a 50 m³ full-scale prototype showing an increase in N-removal rate of up to 3 times that usually achieved in pure MBBR configuration.

Key words

nitrogen removal , Anammox , ANITA™Mox , IFAS , MBBR